This invention relates generally to digital television systems and specifically to an arrangement for improving the luminance signal transient response characteristics and peaking of a digital television receiver.
A digital television receiver described in the ITT publication entitled "Digit 2000-DSLI Digital TV System," which is incorporated by reference herein, describes a digital color television receiver arrangement having a microprocessor that controls a plurality of function control modules over a so-called IM (Intermetall) bus. The luminance signal processing system of the present invention may be utilized with a television receiver constructed in accordance with the above-mentioned publication.
The art has circuits illustrating transient improvement of video signals to compensate for the effects of limited band-width and the like. In U.S. Pat. No. 4,030,121, issued Jun. 14, 1977, a "video crispener" is disclosed for improving the transient response of vide signals. That system developed first and second differentials of an analog input video signal and processing the first differential through a full wave rectifier and the second differential through a limiting amplifier. The products of the rectifier and limiting amplifier were multiplied and added back to the suitably delayed input video signal. Other variants on the above method were also disclosed. The inventive arrangement of the patent, to Applicants' knowledge has never been implemented in video apparatus.
Peaking of video signals has long been done in television receivers in an attempt to enhance the video display by emphasizing certain frequencies of the video signal. Peaking is arbitrary and is based upon subjective criteria as to what constitutes an optimized display. Conventional analog signal peaking techniques are not useful with digital signals however.
The present invention describes apparatus for processing a digitized luminance signal to accentuate or improve transients in the signal and to selectively and variably peak the signal to emphasize low and high frequencies while controlling undershoot and overshoot of the signal. In accordance with the preferred form of the invention, the various parameters for controlling the amount of peaking and transient improvement are factory settings which may be accomplished in software.